Researchers visualize memory formation for the first time in zebrafish

May 16, 2013
The spot-like activities observed in the telencephalon are specific for the long-term memory. Credit: RIKEN

In our interaction with our environment we constantly refer to past experiences stored as memories to guide behavioral decisions. But how memories are formed, stored and then retrieved to assist decision-making remains a mystery. By observing whole-brain activity in live zebrafish, researchers from the RIKEN Brain Science Institute have visualized for the first time how information stored as long-term memory in the cerebral cortex is processed to guide behavioral choices.

The study, published today in the journal Neuron was carried out by Dr. Tazu Aoki and Dr. Hitoshi Okamoto from the Laboratory for Developmental Gene Regulation, a pioneer in the study of how the brain controls behavior in zebrafish.

The is too large to observe the whole neural circuit in action.

But using a technique called calcium imaging, Aoki et al. were able to visualize for the first time the activity of the whole zebrafish brain during .

Calcium imaging takes advantage of the fact that enter neurons upon . By introducing a calcium sensitive fluorescent substance in the neural tissue, it becomes possible to trace the in neurons and thus visualize neural activity.

The researchers trained transgenic zebrafish expressing a calcium sensitive protein to avoid a mild electric shock using a red LED as cue. By observing the zebrafish upon presentation of the red LED they were could visualize the process of remembering the learned .

The fish were trained to learn two opposite avoidance behaviors, each associated with a different LED color, blue or red, as cue. Presentation of the different cues leads to the activation of different groups of neurons in the telencephalon, which indicates that different behavioral programs are stored and retrieved by different populations of neurons. Credit: RIKEN

They observe spot-like neural activity in the dorsal part of the fish telencephalon, which corresponds to the human cortex, upon presentation of the red LED 24 hours after the training session. No activity is observed when the cue is presented 30 minutes after training.

In another experiment, Aoki et al. show that if this region of the brain is removed, the fish are able to learn the avoidance behavior, remember it short-term, but cannot form any long-term memory of it.

"This indicates that short-term and long-term memories are formed and stored in different parts of the brain. We think that short-term memories must be transferred to the cortical region to be consolidated into long-term memories," explains Dr. Aoki.

The team then tested whether memories for the best behavioral choices can be modified by new learning. The fish were trained to learn two opposite avoidance behaviors, each associated with a different LED color, blue or red, as cue. They find that presentation of the different cues leads to the activation of different groups of neurons in the telencephalon, which indicates that different behavioral programs are stored and retrieved by different populations of neurons.

"Using calcium imaging on zebrafish we were able to visualize an on-going process of memory consolidation, for the first time. This approach opens new avenues for research into memory using zebrafish as model organism," concludes Dr. Okamoto.

More information: Aoki et al. "Imaging of Neural Ensembles for Retrieval of Learned Behavioral Programs" Neuron, 2013

Related Stories

Scientists identify mechanism of long-term memory

April 13, 2011

Using advanced imaging technology, scientists from the Florida campus of The Scripps Research Institute have identified a change in chemical influx into a specific set of neurons in the common fruit fly that is fundamental ...

Scientists identify brain's 'molecular memory switch'

March 28, 2013

Scientists have identified a key molecule responsible for triggering the chemical processes in our brain linked to our formation of memories. The findings, published in the journal Frontiers in Neural Circuits, reveal a new ...

Recommended for you

It don't mean a thing if the brain ain't got that swing

July 27, 2015

Like Duke Ellington's 1931 jazz standard, the human brain improvises while its rhythm section keeps up a steady beat. But when it comes to taking on intellectually challenging tasks, groups of neurons tune in to one another ...

Sleep makes our memories more accessible, study shows

July 27, 2015

Sleeping not only protects memories from being forgotten, it also makes them easier to access, according to new research from the University of Exeter and the Basque Centre for Cognition, Brain and Language. The findings ...

Static synapses on a moving structure: Mind the gap!

July 22, 2015

In biology, stability is important. From body temperature to blood pressure and sugar levels, our body ensures that these remain within reasonable limits and do not reach potentially damaging extremes. Neurons in the brain ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.